Thank you for your post.
I have FileMaker Pro 6 and FileMaker Pro 7 both running on my Dell Dimension running Windows XP SP3.
Did you try launching FileMaker Pro 6 prior to upgrading? If so, did that work?
What exact changes were made by the Dell Support Technician?
Do all of your other applications work properly? What other applications are you running?
Any other information you can provide may be helpful.